A technique of converting the optical frequency by making use of cross phase modulation (XPM) that is one of nonlinear optical effects has been known (For example, Japanese Laid-open Patent Publication No. 2017-194576). Another technique of simultaneously converting a wavelength-multiplexed light beam in a wavelength band into a wavelength-multiplexed light beam in another wavelength band by making use of four-wave mixing (FWM) that is one of nonlinear optical effects has also studied and developed.
For example, a related art is disclosed in Japanese Laid-open Patent Publication No. 2017-194576.
In the above-mentioned wide-band wavelength conversion using four-wave mixing, to match the rate of each signal light beam before and after conversion with the rate of excitation light beam, it is required for satisfying phase matching conditions. For example, in the case of wavelength conversion by nondegenerative four-wave mixing using two excitation light beams having different wavelengths, it is required to satisfy the condition that the zero dispersion wavelength is located at the center of each wavelength band before and after conversion and the condition that a dispersion slope is zero in each wavelength band before and after conversion.
However, for example, in consideration of discrepancies in individual pieces, it is difficult to manufacture a dispersion-shifted optical fiber generating four-wave mixing so as to satisfy the above-mentioned two conditions. When the phase matching conditions are not satisfied, a difference occurs between the rate of each signal light beam before and after conversion and the rate of the excitation light beam, disadvantageously lowering the wavelength conversion efficiency.
In light of the above situation, it is desirable to provide a wavelength conversion device, a transmission device, and a transmission system that readily achieve highly-efficient wavelength conversion.